Simpest tip is to be sure the caps are fully down on the nipples. With uncharged/unloaded chambers. put a cap on each nipple..then push the cap with a wooden dowl to be sure it is as far down as it can go. YES...people have managed to set off a cap this way, which is why you test this with an uncharged cylinder (so there is no big boom) and a wooden dowl (so you dont burn the devil out of your finger tip). If fully down and still a no go, then keep reading....if that cures it, then you need better fitting caps (or different nipples to fit the caps you have).
If it still gives trouble...
Holding the empty gun to the side, holding the cylinder FORWARD, take a look at the lowered hammer and the nipple. IF the hammer is toching the nipple or just barely not touching, then it's not the nipple height. IF the hammer face is well away from the nipple AND the cylinder has a good bit of front-to-back movement, then you may not have the wedge driven in far enough.
If the wedge is in tight and the cylinder has little front-to-back movemnt and the hammer still doesn't come close to the nipple, you need new nipples (or check to see if a burr is blocking the hammer from going fully down).
May as well check the hammer to see if it's got any rub marks or dings on the side...if it contacts the frame or cylinder recess before fully lowering, then it wastes it's power and hits the caps too lightly.
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opps..forgot a couple:
Check that the cylinder is in time when the hammer falls...that the bolt (the rectangualr bit that pops up and down under the cylinder) has poped up in one of the locking notches..this locks the cylinder from roations and aligns it with the barrel. IF it's not locked up, it isn't aligned, and the hammer is hitting off center.
BTW: too tight fit between cylinder and barrel (but way of drivng that wedge in too far) can bind them...and bound, you are more likely to not have that cylinder move into alignment.
Mainspring is kind of suspect...but you'd probably notice a too light main spring if you've ever handled a revovler before.